#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <unistd.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <signal.h>

#define BUF_SIZE 100
void error_handling( char *msg);
void read_childproc(int sig);

int main(int argc, char *argv[])
{
    int serv_sock;
    int clnt_sock;
    struct sockaddr_in serv_addr;
    struct sockaddr_in clnt_addr;
    int fds[2];

    pid_t pid;
    struct sigaction act;
    socklen_t adr_sz;
    int str_len;
    int state;
    char buf[BUF_SIZE];

    if (argc != 2) {
        printf("Usage: %s <PORT>", argv[1]);
        exit(1);
    }

    act.sa_handler=read_childproc;
    sigemptyset(&act.sa_mask);
    act.sa_flags=0;
    state=sigaction(SIGCHLD, &act, 0);

    serv_sock=socket(PF_INET, SOCK_STREAM, 0);
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(atoi(argv[1]));

    if (-1 == (bind(serv_sock, (struct sockaddr *) &serv_addr, sizeof(serv_addr)))) {
        error_handling("bind() error");
    }
    if (listen(serv_sock, 5) == -1) {
        error_handling("listen() error");
    }

    pipe(fds);
    pid=fork();
    if (0 == pid) {
        FILE *fp = fopen("echomsg.txt", "wt");
        char msgbuf[BUF_SIZE];
        int i;
        int len;

        for (i = 0;i < 10; i++) {
            len = read(fds[0], msgbuf, BUF_SIZE);
            fwrite((void *)msgbuf, 1, len, fp);
        }
        fclose(fp);
        return 0;
    }

    while (1)
    {
        adr_sz = sizeof(clnt_addr);
        clnt_sock = accept(serv_sock, (struct sockaddr *) &clnt_addr, &adr_sz);
        if (-1 == clnt_sock) {
            continue;
        }
        else {
            puts("new client connected...");
        }

        pid = fork();
        if (0 == pid) {
            close(serv_sock);
            while (0 != (str_len = read(clnt_sock, buf, BUF_SIZE))) 
            {
                write(clnt_sock, buf, str_len);
                write(fds[1], buf, str_len);
            }

            close(clnt_sock);
            puts("client disconnected...");
            return 0;
        }
        else {
            close(clnt_sock);
        }
    }
    close(serv_sock);

    return 0;
}
void read_childproc(int sig)
{
    pid_t pid;
    int status;
    pid=waitpid(-1, &status, WNOHANG);
    printf("removed proc id: %d \n", pid);
}
void error_handling(char *msg)
{
    fputs( msg, stderr);
    fputc('\n', stderr);
    exit(1);
}